1. Field of the Invention
The present invention relates to a normally closed microvalve and, in particular, to such a microvalve providing self-locking action both in case of an overpressure at a fluid inlet of the same and at a fluid outlet of the same. Such a microvalve may be referred to as a normally double-closed microvalve. Such a microvalve is said to be especially suitable for use as an inlet valve in a micropump.
2. Description of the Related Art
From the state of the art, micropumps having passive and active microvalves at the pump inlet and pump outlet are known.
A prior art micropump with passive non-return valves at the pump inlet and pump outlet is for example known from DE-A-19719862 and is shown herein in FIG. 1a to 1c. This pump includes a pump diaphragm wafer 10, in which a pump diaphragm 12 is structured, on which a piezoelectric actuator 14 is provided. Further, the pump includes a first valve wafer 16, in which a valve flap and a valve seat are structured. Further, a second valve wafer 18 is provided, in which a second valve flap and a second valve seat are structured. In the inventive micro-diaphragm pump the three wafers are bonded such that a first non-return valve 20 is deposited between an inlet 22 and a pump chamber 24, and a second non-return valve 26 is deposited between the pump chamber 24 and an outlet 28.
As is shown in FIG. 1b, during a suction stroke, the piezoelectric actuator 14 draws the diaphragm 12 upwards, such that, by means of the negative pressure resulting in the pump chamber 24, a fluid flow occurs through the non-return valve 20 from the inlet 22 in the pump chamber 24.
In a succeeding pressure stroke, the piezoelectric actuator 14 moves the diaphragm 12 downwards, such that, by means of the positive pressure resulting in the pump chamber 24, a fluid flow occurs through the non-return valve 26 in the outlet 28, as is shown in FIG. 1c. As regards further details of such a micropump with passive non-return valves, reference is made to DE-A-19719862 mentioned above.
What is disadvantageous about a micropump with passive non-return valves of the kind described above is that, if a positive pressure is present at inlet 22, the non-return valves 20 and 26 open up, such that an undesired flow, a so-called free-flow, may occur through the pump.
In a multitude of applications, however, such a free-flow is undesired and/or even forbidden. Such applications include any application, the operating conditions of which enable a positive pressure at the inlet and in which, nonetheless, no free-flow is to take place. Applications, in which such a free-flow needs to be avoided in the currentless (non-energized) state, exist, for example, in the field of medical technology or fuel cells.
A further disadvantage of the micropump shown in FIG. 1a to 1c consist in that, for realizing this micropump in a layer-structure, at least three layers are needed, namely the pump diaphragm layer 10 and the two valve layers 16 and 18.
In order to avoid such an undesired free-flow, a number of approaches existed in the state of art. For example, non-return valves were developed, which are biased into the closed position, for example by an appropriate coating on the valve flap. Here, the disadvantage is that, for this purpose, complex processes are required, with appropriate coatings being difficult to realize, especially with the resulting requirements made on a dense wafer connection process. While such biased non-return valves are normally closed, they open at a threshold pressure, i.e. when the inlet pressure exceeds a certain value, such that, by means of such non-return valves, a free-flow may not be excluded in a reliable manner.
Furthermore, it is known from the state of the art, that a normally closed microvalve (a microvalve closed in the non-actuated state) is installed ahead of the inlet of a micro-diaphragm pump with passive non-return valves. Such a solution, as is shown herein in FIG. 2, is disclosed in WO-A-02/27194.
The structure shown in FIG. 2 includes a micro-diaphragm pump 40 with passive non-return valves, as is described above referring to FIG. 1a to 1c. Further, the structure shown there includes a carrier substrate 42 with fluid channels 44, 46 and 48 formed therein. The fluid channel 48 is in fluidic communication to the outlet 28 of the micro-diaphragm pump 40, while the fluid-channel 46 is in fluidic communication to the inlet 22 of the micro-diaphragm pump. The structure shown in FIG. 2 further includes a normally closed microvalve 50, the outlet 52 of which is in fluidic communication to the fluid channel 46 and thus to the inlet 22 of the micro-diaphragm pump 40, and the inlet 54 of which is in fluidic communication to the fluid channel 44. In FIG. 2 the pumping direction is shown by means of arrows 56. As regards the structure of the normally closed microvalve 50, reference is made to the disclosure of WO-A-02/27194 and further to the following description of FIG. 4a to 4d. 
A disadvantage of the FIG. 2 solution of a series-connection between a micropump 40 with passive non-return valves and a normally closed microvalve 50 is the necessary separate component making this solution costly and complex.
Furthermore, micro-peristaltic pumps with integrated active, normally opened valves are known from the state of the art. The advantage of such micro-peristaltic pumps consists in that active closing of the flow path is possible. These pumps, however, are disadvantageous in that they do not lock in the currentless state, since the valves are open in the non-actuated state. Furthermore, peristaltic pumps provide the general disadvantage that several drive elements are needed.
From the above-mentioned WO-A-02/27194 micro-peristaltic pumps with active valves at the inlet and at the outlet are known. Such a micro-peristaltic pump is shown in FIG. 3.
The micro-peristaltic pump shown in FIG. 3 includes two oppositely deposited normally closed valves 60a and 60b. The valve flaps 62 of the normally closed valves 60a and 60b are integrated within a valve flap chip 64. Actuator diaphragms 66 of the two valves 60a and 60b in addition to a pump diaphragm 68 are integrated within a diaphragm chip 70. The chips 64 and 70 are structured to define a pump chamber 72 between the same. On the actuator diaphragms 66 and the pump diaphragm 68, piezoelectric actuators 74, 76 and 78 are provided respectively. The voltages applied to the piezoelectric actuators 74, 76, 78 may be suitably controlled to implement a peristaltic pumping action from the inlet 80 via the pump chamber 72 to the outlet 82. As regards further details of the peristaltic micropump shown in FIG. 3, reference is again made to the disclosure of WO-A-02/27194.
A disadvantage of the micro-peristaltic pump shown in FIG. 3 is, in addition to the requirement of several drive elements, that, in case of great pressure differences during the pressure stroke, the inlet valve cannot be held in a closed state.
A normally closed microvalve, as is respectively used at the inlet of the prior art pumps shown in FIGS. 2 and 3, will be explained in detail below with reference to FIG. 4a to 4d. Further, the disclosure of WO-A-02/27194 regarding the structure and functionality of such a normally closed valve is herewith incorporated.
FIG. 4a shows a bottom view of an actuator chip 100 of the valve, FIG. 4b shows a sectional view along the line x-x in FIG. 4a in the non-actuated state, 4c shows a sectional view along the line x-x in FIG. 4a in the actuated state, and FIG. 4d shows a plan view of a flap chip 102 of the valve. It should be appreciated, that the Figures herein show exemplary structures with chamfered surfaces, as they occur in KOH-etching of silicon substrates, however, with the structures shown allowing to be manufactured in different ways without any chamfered surfaces.
On a first main side 104, the actor chip 100 comprises a depression and/or recess 106, while, on an opposing main side 108, a depression and/or recess 110 is provided. Through the two depressions 106 and 110, an actuator diaphragm 112 is formed. On one side of the actuator diaphragm 112, a piezoelectric ceramic 114 is provided, while a plunger 116 projects on the opposing side of the actuator diaphragm 112. In FIG. 4a, the plunger 116, the depression 110, and, in dotted line, the area of the depression which forms the actuator diaphragm 112 is shown.
The actuator diaphragm 112 and the plunger 116 are formed essentially in a square shape in the lateral direction and are furthermore deposited in a centric arrangement. Further, it can be seen in FIG. 4a, that the diaphragm 112 is surrounded by a sealing lip 120 along three of its four sides and/or edge sections. As can be best seen in FIGS. 4b and 4c, the sealing 120 is formed on the side 108 of the actuator chip 100 and is preferably structured at the same time with the plunger 116. The flap chip 102 is connected to the actuator chip 100 and includes an outlet area 130 and an inlet channel area 140. The outlet area 130 includes an outlet opening 132 completely penetrating the flap chip 102, while the inlet channel area 140 includes an inlet opening 142, which completely penetrates the flap chip 102 as well. The inlet channel area 140 is formed by means of a depression in the second main side of the flap chip 102, which extends up to a closing flap and/or a flap diaphragm 150.
The closing flap 150, as is shown in FIG. 4d, is formed in a square shape and is freely moveable on three from four of its sides and/or edges by the inlet opening 142 relative to remainder of the flap chip 102, while the same being mounted and/or fixed to the fourth side. The valve flap 150, along its lateral expansion, extends a bit beyond the lateral expansion of the sealing lip 120, such that the inlet opening 142 and the inlet channel area 140 in the normally closed state of the valve are laterally limited by the flap chip 102 and against the outlet area 130 by the valve flap 150, the sealing lip 120, and a part of the depression 110 surrounding the sealing lip 120.
In the normally closed valve shown in FIG. 4a to 4d the closing flap 150 is deposited such that the lateral dimensions of the closing flap 150 are greater than the surrounding sealing lip 120 of the actuator chip 102, and that the inlet pressure exerted by a fluid to be switched in the inlet channel area 140 onto the closing flap 150 adjoining the inlet channel area 140, provides a closing action. Without applying any voltage to the piezoelectric ceramics 114 and, therefore, without applying any pressure to the closing flap 150, the closing flap is consequently closed. For opening the valve, a voltage, which is positive into the polarization direction, is applied to the silicon-piezo bending converter, which is formed by the piezoelectric ceramics 114 and the diaphragm 112, as a result of which the silicon-piezo bending converter, together with the plunger 116 pushes open the closing flap 150 against the inlet pressure, see FIG. 4c. More precisely, the diaphragm 112 together with the plunger 116 is moved into the direction of the valve flap 150 by means of the positive voltage applied in polarization direction to the piezoelectric ceramics 114, with the valve flap bending open owing to the pressure of the plunger 116 and forming a space 152 between itself and the sealing lip 120.
The self-locking active microvalve described above with reference to FIG. 4a to 4d, has the quality of locking when a positive pressure is applied to the inlet 140. A reference pressure acting onto the diaphragm 112 from the opposing side of the valve flap 150 and which is typically the atmospheric pressure tends to provide an opening action for the microvalve. Further, it has turned out that in the microvalve described in WO-A-02/27194, a positive pressure at the outlet 130 tends to provide an opening action to the valve. If, therefore, this valve is used as a sole inlet valve of a micropump, with the output 130 being in a fluidic communication to the pump chamber of the micropump, a return-flow may occur through the inlet valve during a pumping phase, during which a positive pressure prevails in the pump chamber.